Polymeric roof sheeting materials such as ethylene-propylene-diene terpolymer (EPDM), butyl rubber (IIR), neoprene, polyvinyl chloride, chlorinated polyethylene, thermoplastic polyolefin rubber and modified bitumen and the like are used as single ply roofing membranes for covering flat roofs typically found on industrial or commercial buildings. Such roofing membranes are customarily large elastomeric sheets which must be seamed or spliced together on the rooftop during installation. However, because these elastomeric (EPDM, neoprene and butyl-based, etc.) roofing membrane compositions are typically cured prior to being installed on a roof, they generally lack the ability to adhere to one another. Further, the seam or area of overlapping of the roof sheeting materials is subject to both short-term and long-term stresses such as those caused by roof movement, heavy winds, freeze-thaw cycles and thermal cycles. Such stresses may manifest themselves in shear forces or peel forces, i.e., the seam peels back under severe stress conditions or may cause a partially open seam (often referred to as a fish-mouth condition) under less severe conditions.
A variety of methods for adhering or seaming the roofing membranes together have been developed over the years. For example, solvent-based adhesives, which typically employ neoprene or butyl-based compounds, have been used to bond roof sheeting materials together by applying, with a brush or other similar means, the liquid or paste-like adhesives directly to the edge areas of the roofing membranes to be joined. However, these adhesives have limited storage life, and are highly toxic and flammable, making them environmentally undesirable. Moreover, application of these adhesives to the roof sheeting membranes is often time-consuming and requires skill in applying the adhesive evenly since streaking and uneven coatings are known to reduce bond strength between the adhesive and the rubber sheeting material.
Alternatively, uncured polymeric tapes containing no vulcanizing agents, i.e., non-curable tapes, have been developed. However, these tapes never cure, even after installation, and therefore, creep under stress is a significant problem associated with the use of these tapes on roofs.
Another type of adhesive composition often used for joining roofing sheet membranes together are those which are initially unvulcanized but which contain curatives so as to be vulcanizable. These adhesives, commonly referred to as rooftop curable adhesives, are typically used in the form of a preformed tape to bond sheet membranes and the like together. However, it is well known that, because the rooftop curable adhesives are uncured when initially installed on a roof, they are recognized as having low initial strengths and are not easily handled. Moreover, some rooftop curable adhesives can take several days or even weeks to achieve good adhesion.
To facilitate adhesion, some of these adhesives may include heat-activated or fast-acting cure systems. Those adhesives with fast-acting cure systems will require additional equipment to blend and extrude the tape mixture to prevent premature curing which can adversely affect the adhesive properties of the composition when applying the adhesive tape to the rooftop membranes. Those adhesives with heat-activated cure systems also will require comparable equipment at the job site to provide the necessary heat and pressure to the tape for joining the sheet membranes together.
Thus, it should be evident that only after an extended period of exposure to high rooftop temperatures or upon application of heat and pressure at the rooftop site is vulcanization achieved to provide the necessary peel and shear strengths required to prevent the seams from sliding or opening. Further, in order to obtain good adhesion, heat and pressure must be applied over a relatively lengthy period of time, thus increasing the time necessary for installation of the sheet membranes on the roof.
Accordingly, attempts have been made in the art to develop adhesive tape compositions which are easier to apply between the area of overlapping of the rubber sheeting membranes, and which provide sufficient seam peel and shear strengths to permit the splice formed by the bonding of the rubber sheeting membranes to withstand and resist heat aging and moisture penetration and other problems such as oxidation, hydrolysis and chemical attack from pooled water, as well as other short-term and long-term stresses as noted hereinabove. Unlike rooftop curable adhesives, these preformed adhesive tapes are at least partially cured prior to being installed upon the roof. Thus, they are far more deformation resistant and easier to handle than the unvulcanized, but vulcanizable adhesives noted hereinabove. These adhesives are also easier to remove from the release paper upon which they are stored prior to use. Nevertheless, these adhesives have the ability to adhere the roofing sheets together, with minimal pressure. Thus, these preformed adhesive tapes, and the adhesive tapes of the present invention, are often referred to as pressure sensitive adhesives.
In order to provide adhesion and a watertight seal between the tape and the rubber sheeting upon contact, these adhesive tapes typically include a tackifying additive compatible with the rubber employed such as polybutene. It has been found that polybutene, when used with a butyl rubber composition, provides an adhesive tape having sufficient surface tack and "quick-grab" as well as adequate green strength for use in adhering roofing sheet membranes together.
Accordingly, heretofore, most pressure sensitive adhesives used to join rubber roofing membranes together included a rubbery polymer composition based on butyl rubber or butyl rubber blended with various amounts of EPDM. The cured adhesive also included a cure package, typically based upon the use of a sulfur, peroxide or quinoid crosslinking system.
For example, Chiu U.S. Pat. Nos. 4,588,637, 4,855,172 and 5,095,068 disclose adhesive compositions, prepared in the form of a cured adhesive tape, which comprises butyl rubber-based compositions made by compounding a butyl rubber, a curing agent for the butyl rubber, carbon black, and a compatible tackifying additive.
Metcalf et al. U.S. Pat. No. 4,601,935 discloses a seaming tape comprising a carbon black-reinforced, compounded, lightly cured blend of a butyl rubber and a polyisobutylene. The seaming tape serves to adhere the primer-coated seam edges of EPDM membranes together.
Briddell et al. U.S. Pat. No. 5,242,727 discloses a cured adhesive tape composition which includes substantially equal amounts by weight of a rubbery polymer comprising a blend of EPDM, a halogenated butyl rubber or a halogenated isobutylene-based copolymer and polyisobutylene, a compatible tackifying additive and a compatible accelerator/cure package for the rubbery polymer blend.
It is clear that all of the above adhesive tape compositions include butyl rubber (IIR). The term "butyl rubber" as used herein is intended to include copolymers of isobutylene and isoprene as well as other rubbery copolymers comprising at least 50 percent by weight of an isoolefin having 4 or more carbon atoms and 50 percent or less by weight of an open chain conjugated diolefin having from 4 to 8 carbon atoms. "Butyl rubber" is intended to also include halogenated butyl rubber, such as chlorobutyl or bromobutyl rubber, as well as those types of butyl rubber in which conjugated diene functionality has been added in the linear backbone at the diolefin units, such as more particularly described in U.S. Pat. No. 3,816,371.
Butyl rubber is used in these adhesive tape compositions to enhance surface tack required for joining together two overlapped single-ply EPDM roofing membranes. However, butyl rubber tape compositions do not provide as good long-term aging and weather resistance properties as tape compositions based upon ethylene-propylene-diene terpolymers (EPDM). Moreover, EPDM-based tape compositions exhibit good low temperature properties as compared to butyl-based tape compositions and would clearly be more compatible with EPDM membranes and flashing materials.
Some patents have recognized the use of EPDM in tape compositions. For example, Fujuki et al. U.S. Pat. No. 4,379,114 discloses a curable tape which may include a vulcanizable, but unvulcanized EPDM rubber, butyl rubber, or a blend thereof. The curable tape may further include a vulcanizing agent and accelerator, a softening agent, and other ingredients such as fillers and the like.
Kakehi et al. U.S. Pat. No. 4,404,056 discloses a cold-vulcanizable adhesive tape having a Mooney viscosity of from about 5 to 25 and which includes a rubbery polymer comprising EPDM, butyl rubber or a blend thereof, as well as a vulcanizing agent, a vulcanization accelerator, an adhesive (tackifying) agent and a softening agent.
Westley U.S. Pat. No. 4,581,092 discloses a preformed adhesive tape composition comprising EPDM or halogenated butyl rubbers, at least one polyisocyanate, a low-temperature and a high-temperature tackifying additive, and at least one curing agent.
It will be appreciated, however, that the rubbery components of the adhesive tapes noted hereinabove comprise essentially 100 percent EPDM rubber, 100 percent butyl rubber or a blend of EPDM and butyl rubber. As noted hereinabove, butyl rubbers do not provide as good long-term aging and weather resistance properties as tape compositions based upon ethylene-propylene-diene terpolymers (EPDM). However, 100 percent EPDM compositions do not have very good surface tack, initial strength or "quick-grab". "Quick-grab" refers to the characteristic of the adhesive tape composition to develop immediate adhesion when placed in direct contact with the surface of cured sheets of polymeric roof sheeting material.
Thus, it should be clear that the EPDM-based adhesive compositions described hereinabove suffer from a significant disadvantage which materially limits their usefulness as pressure sensitive adhesives for bonding cured, elastomeric roof sheeting membranes together. While attempts may have been made heretofore to provide adhesive tape compositions which improve some of the properties in either 100 percent EPDM rubber-based or butyl rubber-based adhesive tape compositions, the need still exists in the art for an effective EPDM rubber-based adhesive tape composition and method of application for use in adhering together rubber sheets and for covering roofs which provide easy application, excellent peel and shear seam strength, excellent initial adhesive strength and "quick-grab" and better surface tack, and maintain long-term heat aging and weather resistance.